The present invention relates to an improvement made to plants used for treating sheet materials by means of pressurized water jets, which act on the structure in the manner of needles, the latter being used in particular for treating nonwoven structures for the purpose of giving them cohesion and/or modifying their appearance.
Such a technique, which has been used for decades, as is apparent for example from patents U.S Pat. Nos. 3,214,819 and 3,485,706, consists in subjecting the sheet structure to the action of water jets coming from one or more successive injector rails, the web being supported by a porous or perforated conveyor belt or rotating roll, said belt or roll being subjected to a suction source allowing the water to be recovered.
One of the essential elements of such plants is the system for forming the water jets or needles, this commonly being referred to by the expression xe2x80x9cinjectorxe2x80x9d.
The invention relates more particularly to a novel type of injector.
The injectors used at the present time may be produced specifically in accordance with the teaching of FIG. 42 of patent U.S. Pat. No. 3,485,706 and of the corresponding passages from the description of that document, and the much more detailed specific embodiments appearing for example in patent U.S Pat. No. 3,613,999 and in EP 400 249 (corresponding to U.S. Pat. No. 5,054,349), the latter document describing a type of injector which not only makes it possible to inject water at a very high pressure (greater than 100 bar) but has a structure such that it allows the perforated plate, through which the microjets pass, to be easily fitted and removed.
Referring to the appended FIG. 1, such injectors are therefore in general in the form of a continuous injector rail which extends transversely with respect to the direction of movement of the sheet material (F), for example a nonwoven, to be treated and the length of which is matched to the width of the said material. This injector rail may consist of a single individual module or a plurality of mutually juxtaposed modules.
Such an injector rail is composed of a main body (1) which can withstand any deformation due to the water pressure and in the upper part of which there is a chamber (2), in general of cylindrical shape, fed with pressurized water through a pipe (3) supplied via a pump (not shown). Placed inside the chamber (2) is a cartridge (4) consisting, for example, of a perforated cylinder lined with a filter cloth which not only acts as filter but also as distributor.
The pressurized water fed into the chamber (2) then flows through cylindrical holes (5) which are separated with a regular pitch over the entire width of the injector, the diameter of which holes is in general between 4 mm and 10 mm and the thickness of the wall between two consecutive holes being around 3 to 5 mm.
These cylindrical holes (5), the outlet end of which may possibly be of conical shape, then emerge in a lower chamber (6) at the base of which a plate (7) provided with microperforations is positioned, the diameter of the microperforations of which may be between 50 and 500 xcexcm and preferably between 100 and 200 xcexcm, making it possible to form water jets or needles (8) which act directly against the surface of the material (F) to be treated, for example a nonwoven web.
The perforated plate (7) is held against the main body of the injector by, in accordance with the teaching of EP 400 249 for example, longitudinal jaws (9) subjected to the action of hydraulic cylinders which allow a clamping action to be exerted by means of a system of cross bars and pull rods placed along the injector.
A seal (not shown) is placed between the perforated plate (7) and the base of the main body (1).
Such a system for distributing pressurized water against the microperforated plate intended to form the water needles, and which therefore makes use of holes (5) emerging in a lower chamber (6), makes it possible to distribute the water correctly over the entire length of the injector, the same amount of water passing through each orifice.
However, it has been found that such a solution, especially in the case of the treatment of nonwoven webs, can result in defects in the treated product when the water pressure in the injector exceeds 50 bar.
FIG. 2 illustrates schematically the reasons for such defects.
This figure shows that, when the water feed pressure inside the cylindrical bore (2) is increased, this being essential when it is desired to increase production rates and/or treat heavy products, areas of turbulence are produced in the lower chamber (6) in those regions (10) lying immediately below the walls separating two consecutive holes (5). Such turbulence is transmitted to the water jets, resulting in a substantial and rapid reduction in their energy, the jets (J1) becoming diffuse and whitish beneath the said areas of turbulence, whereas under the holes (5) the flow from the jets (J2) remains unidirectional, stable and turbulence-free.
During the treatment of nonwoven webs, such a disparity in flow has immediate repercussions on the effectiveness of fiber bonding and makes the entanglement of the fibers in the product heterogeneous, particularly with a variation in density.
Consequently, as shown schematically in FIG. 1, low-density bands (B) are obtained on the finished product, these bands being very irregular surfacewise and coinciding exactly with the turbulent flow regions between the holes.
An improvement to such a type of injector has now been found, and it is this which forms the subject of the present invention, which makes it possible to solve this problem and allows water to be supplied with a high pressure, possibly reaching 400 bar or more, and which makes it possible to obtain a stable and turbulence-free flow of pressurized water between the pressurized-water feed chamber and the perforated plate for forming the treatment jets or needles, the said jets being perfectly homogeneous and all having the same action on the product to be treated.
In general, the injector according to the invention, therefore allowing the treatment of a sheet material (nonwoven, textile complex, film, paper, etc.) by means of water jets/needles, comprises:
a body for supplying pressurized water, comprising a feed chamber which extends over the entire length of said body and inside which the pressurized water is taken through a filter;
a distribution region, distributing the pressurized water over the entire treatment width against a plate provided with microperforations, the holes of which define water needles directed against the surface of the material to be treated, said material being supported by a transporter element (drum or conveyor belt) subjected to a suction source allowing the treatment water to be removed, and it is characterized in that the water is transferred from the feed chamber to the perforated plate via a channel of rectangular cross section extending over the entire length of the injector, from the periphery of the feed chamber to the surface of the perforated plate, the separation between the side walls of this channel and its height producing a unidirectional, stable and turbulence-free flow of water.
To obtain such laminar flow of the pressurized water, the space between the two side walls defining the distribution channel is advantageously between 2 mm and at most 10 mm, the height of the walls being between 5 mm and 100 mm and the jets produced by the microperforations having, thanks to such a structure, an identical output energy over the entire treatment width.